Electrolytic process of producing purine derivatives



United States Patent N l YFL NHz and ll R1 Y NH,

wherein X and Y respectively represent the same or different members selected from the group consisting of H, lower alkyl, OH, NH lower alkylamino, lower alkylmercapto and SH; only one of X and Y, is OH at any one time; X and Y represent the same or different members selected from the group consisting of NH, O and S; the R substituents are no more than three in number and are in the 2-, 3-, 4-, 5- and/or 6-positions of the benzene nucleus and may be same, partly different or entirely different substituents selected from the group consisting of H, lower alkyl, hydroxyl, lower alkoxy, halogen, nitro, sulfo (-SO H) and carboxyl radicals; and R and R represent the same or ditferent lower alkyl groups, through a series of reactions of electrolytic reduction, formylation and ring-closure that may be carried out continuously in a single stage in a solvent containing formic acid, no isolation of intermediate product being required.

Prior known processes for the production of purine derivatives from 4-amino-5-arylazopyrimidine derivatives entail the disadvantages of requiring more than a single step, conditions including high temperatures and high pressures, and sometimes involving intermediates susceptible to oxidation and discoloration, such as 4,5,6-triaminopyrimidine.

" The present invention embodies methods of producing e.g. hypoxanthine and adenine, which are free from the aforesaid disadvantages, thus providing commercially feasible processes of producing hypoxanthine from 4-amiice no-S-arylazo-6-hydroxypyrimidine and adenine from 4,6- diamino-S-arylazopyrimidine, respectively, in high yield and continuously in a single stage through electrolytic reduction. Moreover, the same principle can be applied to embody commercially advantageous processes for the single step production of guanine, isoguanine, 2,6-diaminopurine, Xanthine and other purine derivatives from corresponding 4-amino-S-arylazopyrimidine derivatives.

One embodied process of this invention comprises introducing a starting material of this invention, 4-amino- S-arylazopyrirnidine, into a suitable electrolyte containing formic acid, effecting electrolytic reduction of the arylazo group at a suitable temperature using a suitable electrode and an electric current with a suitable density while stirring the solution, heating the reaction mixture to higher temperatures for inducing closure of imidazole ring (formation of purine ring) and recovering corresponding purine derivative in high yield.

Suitable anodes may be selected from among tungsten, tantalum, lead, palladium, iridium, gold, platinum and carbon anodes which have low ionization tendency; and suitable cathodes may be selected from among carbon, amalgamated zinc, copper, iron, amalgamated cadmium, tantalum, lead, lead dioxide, mercury, silver, gold, platinum, palladium, iridium, rhodium, nickel, molybdenum, tungsten cathodes and cathodes of alloys containing one or more of these. The most economical combinations are an anode consisting of carbon, lead or platinum and a cathode consisting of carbon, lead, platinum, mercury, copper, iron or an alloy containing one or more of these materials.

The process of this invention may be represented by the following reaction scheme:

or a mixture thereof wherein X Y and R are as defined above.

In the present invention, the first step reaction, electrolytic reduction, is preferably carried out at temperatures above C. to enhance the smooth progress of the succeeding formylation reaction, although ordinary temperatures are not objectionable. The said electrolytic reduction proceeds at a velocity substantially proportional to the amount of electric current. The operation conditions comprising voltage and density of electric current may be varied over a wide range according to the shape of equipment and operation period.

For the purpose of smoothly carrying out the process of this invention, a suitable solvent or diluent is advantageously used. Furthermore, a suitable solvent forming an azeotrope with water may be added to remove the water generated during the reaction.

Although the process of this invention is preferably carried out in an inert atmosphere such as nitrogen, even the reaction in air is capable of yielding sufiiciently pure purine derivatives.

The purine derivatives thus produced are very important products as starting materials for the production of chemical flavoring agents, e.g., 5-inosinic acid, etc., and pharmaceutical products.

The following illustrative, but non-limitative, examples set forth presently preferred embodiments of this invention. Therein, parts by weight bear the same relation to parts by volume as do grams to milliliters.

Example 1 A stirred cathode liquor consisting of 5.3 parts by weight of 4-amino-5-phenylazo-6-hydroxypyrimidine suspended in 150 parts by volume of 50% aqueous formic acid is electrolytically reduced for about 2.5 hours using a lead plate (surface area 27.0 cm. for each 150 parts by volume of liquor), a carbon plate as an anode and an electric current with a density of 50-60 amperes/dmF, at a temperature of 90-105 C. until the color of the raw material disappears and the suspension becomes clear. Thereafter, the reaction mixture is heated and refluxed for about 8 hours and the resulting dark brown solution is concentrated in vacuo to a volume of 30-50 parts by volume. The concentrate is poured into 200-300 parts by volume of water and filtered while hot. The filtrate is treated with activated carbon, concentrated to a volume of 50-70 parts by volume, allowed to stand while being cooled. The resulting white precipitate is collected by filtration. Yield of hypoxanthine: 2.5 parts by weight.

Elemental analysis.Calculated for C H N O: C, 44.12; H, 2.96; N, 41.17. Found: C, 44.36; H, 3.05; N, 41.33.

Example 2 A stirred cathode liquor containing 5.5 parts by weight of suspended 4-amino-5-phenylazo-6-hydroxypyrimidine in a mixture of 150 parts by volume of 90% formic acid and 50 parts by volume of formamide is electrolytically reduced for about 2.5-3 hours using a lead plate (surface area: 27.0 cm? for each 150 parts by volume of liquor) as a cathode, a carbon plate as an anode and electric current with a density of 50-60 a./dm. at a temperature of 90-105 C. The resulting clear solution is heated while distilling low boiling fractions and is then maintained at 165 -l70 C. for about 1 hour. The resulting dark brown reaction mixture is concentrated in vacuo to a volume of -20 parts by volume and the concentrate is poured into 200-300 parts by volume of Water and filtered while hot. The filtrate is treated with activated carbon while hot, concentrated to 50-70 parts by volume and allowed to stand overnight while being cooled. The separating grayish white precipitate is collected by filtration. Yield of hypoxanthine: 2.9 parts by weight.

Example 3 A cathode liquor containing 5.4 parts by weight of suspended 4,6-diamino-5-phenylazopyrimidine in a mixture of 150 parts by volume of 90% formic acid and 50 parts by volume of formamide is treated as described in Example 2, using a lead plate (surface area 27.0 cm. for each 200 parts by volume of liquor) as a cathode and a carbon plate as an anode to yield 2.7 parts by weight of free adenine.

Elemental analysis.-Calculated for C H N C, 44.44; H, 3.73; N, 51.83. Found: C, 44.64; H, 3.96; N, 51.98.

Example 4 A cathode liquor containing 5.8 parts by weight of suspended 4amino-6-hydroxy-5-(p-methylphenylazo)-pyrimidine in a mixture of 7.5 parts by Weight of sodium carbonate, 150 parts by volume of 90% formic acid and 50 parts by volume of formamide is stirred and electrolytically reduced for 3.03.5 hours using mercury as a cathode (surface area 88.5 cm. for each 200 parts by volume of liquor), thick platinum wire as an anode, an anode solution containing 2.5 parts by weight of sodium carbonate in 25 parts by volume of water placed in a porous cylinder, an electric current with a density of 0.8-1.5 a./dm. at an electrolysis temperature of 90 105 C. The treatment as set out in Example 2 gives 2.5 parts by weight of free hypoxanthine.

Example 5 A suspension of 5.5 parts by weight of 2,4-diamino-6- hydroxy-S-phenylazopyrimidine treated as in Example 2 using lead plate as a cathode (surface area 27.0 cm. per 150 parts by volume of liquor) and carbon plate as an anode gives 2.9 parts by weight of free guanine.

Elemental analysis.-Calculated for C H N O: C, 39.73; H, 3.33; N, 46.34. Found: C, 39.95; H, 3.53; N, 46.70.

Example 6 A stirred cathode liquor containing 5.5 parts by weight of 2,4-diamino-6-hydroxy-5-(p nitrophenylazo) pyrimidine suspended in a mixture of 7.5 parts by weight of sodium carbonate, 150 parts by volume of 90% formic acid and 50 parts by volume of formamide is electrolytically reduced for 2.5 to 3.5 hours, using mercury as a cathode (area 88.5 cm. per 200 parts by volume of liquor) and a thick platinum wire as an anode, an anode solution containing 2.5 parts by weight of sodium carbonate in 25 parts by volume of water placed in a porous cylinder and an electric current with a density of l-3 a./dm. at an electrolysis temperature of 90-l05 C. The after-treatment as described in Example 2 gives 2.7 parts by weight of free guanine.

Example 7 A stirred cathode liquor consisting of 2.4 parts by weight of 4,6-diamino-5-(o methoxyphenylazo) pyrimidine suspended in a mixture of 150 parts by volume of 90% formic acid and 50 parts by volume of formamide is electrolytically reduced, using copper plate (surface area: 36.0 cm. per 200 parts by volume of liquor) as a cathode and a platinum wire as an anode, an electric current at the cathode with a density of 30-40 a./dm. and an electrolysis temperature of 90105 C. The aftertreat-ment as in Example 2 gives 0.8-l.0 part by weight of adenine.

Example 8 A stirred cathode liquor consisting of 4-amino-6-hydroxy-5-phenylazopyrimidine (5.5 parts by weight) in 200 parts by volume of formic acid is reduced for about 2.0-3.0 hours using lead plate (surface area: 27.0 cm. per 200 parts by volume of liquor) as a cathode, carbon plate as an anode and an electric current with a density of 55-60 a./dm. at a temperature of l05 C. The resulting reaction mixture is heated to distill off -150 parts by volume of water and formic acid, 50 parts by volume of formamide added, and refluxed for about 2 hours. The reaction mixture is concentrated in vacuo and treated as in Example 2 to yield 2.6 parts by weight of hypoxanthine.

The following compounds gave corresponding purine derivatives when treated as described above, in this example:

(1) Isoguanine from 4,6-diamino-2-hydroxy-5-phenylazopyrimidine (yield: 81%).

(2) 2,6-diaminopurine from 2,4,6-triamino-5-phenylazopyrimidine (yield: 80%).

(3) 2 aminopurine from 2,4 diamino 5-phenylazopyrimidine (yield: 75%

(4) 2 diethylaminopurine from 4 amino 2-diethylamino-5-phenylazopyrimidine (yield: 75

(5) Z-methylhypoxanthine from 4-amino-6-hydroxy-2- methyl-5-phenylazopyrimidine (yield: 76%).

(6) 2 hydroxy 6 methylpurine from 4-amino-2-hydroxy-6-methyI-S-phenylazopyrimidine (yield: 71%

(7) 2 amino 6 methylpurine from 2,4 diarnino-6- methyl-5-pheny1azopyrimidine (yield: 74%).

(8) Z-mercaptoxanthine from 4-amino-6-hydroxy-2- mercapto-5-phenylazopyrimidine (yield: 75

(9) Z-mercaptoadenine from 4,6-diamino-2-mercapto- S-phenylazopyrimidine (yield: 80%).

(10) 2-methylmercaptoadenine from 4,6-diamino-2- methylmercapto-5-phenylazopyrirnidine (yield: 79%).

(11) Z-methylguanine from 2,4-diamino-3,6-dihydro- 3-methyl-6-oxo-5-phenylazopyrimidine (yield: 81%) (12) 1,3 diethylxanthine from 4 amino 1,3-die thyl- 1,2,3,6 tetrahydro 2,6 dioxo 5 phenylazopynmidine ield: 72%). I (13) hypoxanthine from 4-amino-6-hydroxy-5(2,4,5 trimethylphenylazo)-pyrimidine (yield: 73%). D

(14) Adenine from 4,6 diamino 5(3,5' dimethylphenylazo)-pyrimidine (yield: 76%).

(15) Guanine from 2,4-diamino-6-hydroxy-5-(p-sulfophenylazo)-pyrimidine (yield: 78%

(16) Hypoxanthine from 4-amino-5-(2,4-dichlor0- phenylazo -6-hydroxypyridimidine (yield: '78

(17) Guanine from 5 (p carboxyphenylazo)-2,4-diamino-6-hydroxyprimidine (yield: 80%

What is claimed is: I

1. In a process of producing purine derivatives where in a 4-amino-5-arylazopyrimidine of one of the formulae wherein each of X and Y is a member selected from the group consisting of H, lower alkyl, OH, NH lower alkylamino, lower alkylmercapto and SH; each of X and Y is a member selected from the group consisting of NH, O and S; R is a member selected from the group consisting of H, lower alkyl, hydroxyl, lower alkoxy, halogen, nitro, sulfo and carboxy; each of R and R is lower alkyl; and n is one of 0, 1, 2 and 3; only one of X and Y being OH at any one time, is subjected to reduction and imidazole ring closure, the improvement according to which the reduction is electrolytic reduction and is effected together with imidazole ring closure in an electrolyte containing formic acid without separa ion of any formed intermediate.

2. The improvement according to claim 1 wherein 4-amino-5-phenylazo-6-hydroxypyrimidine is subjected to electrolytic reduction in an electrolyte constituted by aqueous formic acid, and the resultant hypoxanthine is recovered from the reaction mixture.

3. The improvement according to claim 1 wherein 4-amino-5-phenylazo-6-hydroxypyridine is subjected to electrolytic reduction in an electrolyte constituted by aqueous formic acid and formamide, and the resultant hypoxanthine is recovered from the reaction mixture.

4. The improvement according to claim 1 wherein 4,6- diamino-S-phenylazopyrimidine is subjected to electrolytic reduction in an electrolyte constituted by aqueous formic acid and formamide, and the resultant adenine is recovered from the reaction mixture.

5. The improvement according to claim 1 wherein 4-amino-6-hydroxy-5- p-methylphenylazo -pyrimidine is subjected to electrolytic reduction in an electrolyte constituted by aqueous formic acid, and the resultant hypoxanthine is recovered from the reaction mixture.

6. The improvement according to claim 1 wherein 2,5-diamino-6 hydroxy 5 phenylazopyrimidine is subjected to electrolytic reduction in an electrolyte constituted by aqueous formic acid and formarnide, the resultant guanine is recovered from the reaction mixture.

7. The improvement according to claim 1 wherein 2,4-diamino-6-hydroxy-5-(p-nitrophenylazo) pyrimidine is subjected to electrolytic reduction in an electrolyte constituted by aqueous formic acid and formamide, the resultant guanine is recovered from the reaction mixture.

8. The improvement according to claim 1 wherein 4,6-diamino-5-(o-methoxyphenylazo)-pyrimidine is subjected to electrolytic reduction in an electrolyte constituted by aqueous formic acid and formamide, and the resultant guanine is recovered from the reaction mixture.

References Cited UNITED STATES PATENTS 3,252,876 5/1966 Koehl 20459 3,252,877 5/1966 Koehl 20459 3,321,387 5/1967 Koehl 204-72 JOHN H. MACK, Primary Examiner.

H. M. FLOURNOY, Assistant Examiner. 

1. IN A PROCESS OF PRODUCING PURINE DERIVATIVES WHEREIN A 4-AMINO-5-ARYLAZOPYRIMIDINE OF ONE OF THE FORMULAE 